1. Field of the Invention
The present invention generally relates to a passive optical network (PON) and, in particular, to a Gigabit-Ethernet controller for use in an optical-network unit (ONU) of a Gigabit Ethernet-passive optical network (GE-PON).
2. Description of the Related Art
A PON system, which is an optical-subscriber network that is based on passive devices, has an architecture made of passive-distribution devices or wavelength-division-multiplexing (WDM) devices between a subscriber-access node, such as fiber-to-the-home (FTTH) or fiber-to-the-curb (FTTC), and a network termination (NT), in which all the nodes are distributed in the form of a bus or tree structure.
An asynchronous-transfer mode (ATM)-PON is an exemplary PON system and explained in detail in the International Telecommunication Union-T (ITU-T) G983.1. The standardization on the media-access-control (MAC) technology of the ATM-PON has been completed and is readily available. This type of technology is also well disclosed in other publications—for example, in U.S. Pat. No. 5,978,374, issued on Nov. 2, 1999, entitled “Protocol for Data Communication over a Point-to-Multipoint Passive Optical Network,” and Korean Patent Application No. 1999-70901, published on Sep. 15, 1999, entitled “Protocol for an Asynchronous Transfer Mode Passive Optical Network Media Access Control.”
With the development of the Internet technology, many subscribers have been demanding more bandwidth for their applications. To this end, the GE-PON system, which has relatively low costs, has been developed to provide more bandwidth during the end-to-end transmission using Gigabit Ethernet. As such, the demand is growing for the GE-PON system over an ATM system; however, this system has relatively high costs, limited bandwidth, and undesirable segmentation of an Internet-protocol packet.
FIG. 1 is a general schematic block diagram of a GE-PON. As shown, an optical line terminal (OLT) 100 is connected to a plurality of optical-network units (ONUs) 104 via an optical-distribution network (ODN) 102 using an optical splitter. Here, the OLT 100 and ONUs 104 constitute the Gigabit Ethernet. The ONU 104 is typically installed at the distribution boxes within buildings or apartment blocks, or at the entrances of houses, and connected to a network of terminals (not shown). The OLT 100 receives data from a backbone network and transmits the data to the ONUs 104 via the ODN 102 or receives data from the ONU 104 using the time-division-multiplexing (TDM) protocol.
A Gigabit-Ethernet controller must be used in the ONU 104 for a point-to-point communication. Commercially available Gigabit-Ethernet controllers are shown, for example, in FIGS. 2 and 3. As shown in FIG. 2, a Gigabit-Ethernet controller 200 includes a media-access controller (MAC) 202 and a physical-coding sublayer (PCS) 204. Similarly, as shown in FIG. 3, a Gigabit-Ethernet controller 300 includes a MAC 302, a PCS 304 and a serializer/deserializer (SERDES) 306. Unlike the Gigabit-Ethernet controller shown in FIG. 3, the Gigabit-Ethernet controller depicted in FIG. 2 must have a SERDES 206 connected to the PCS 204. An optical transceiver (not shown) is connected to the SERDESs 206 and 306 and transmits an optical signal to the OLT 100 in response to data generated from the SERDESs 206 and 306 while converting an optical signal generated from the OLT 100 into electric-signal data.
During operation, if there is no data transmission, the Gigabit-Ethernet controllers 200 and 300 automatically generate idle-pattern data instead of transmitting data in the PCSs 204 and 304. The idle-pattern data alternates between the logic “0” and “1”, that is “101010 . . . .” Thus, if the Gigabit-Ethernet controllers 200 and 300 are implemented in the GE-PON, data collision may occur as some ONUs may transmit the idle-pattern data while other ONUs exchange data with the OLT 100. The data collision leads to a loss of upstream data transmitted to the OLT 100.
As such, the conventional Gigabit-Ethernet controller can not be used in the GE-PON structure that is based on the point-to-multipoint communication. Accordingly, there is a need for a new Gigabit-Ethernet controller that overcomes the above-stated problems.